The present invention relates to a heat-developable photosensitive material, in particular, an ultrahigh contrast heat-developable photosensitive material. More specifically, the present invention relates to a heat-developable photosensitive material which causes almost no fog (Dmin), in particular, an ultrahigh contrast heat-developable photosensitive material which exhibits low Dmin and is suitable for photomechanical reproduction.
A large number of photosensitive materials are known which have a photosensitive layer on a support and form image by imaging exposure. An example of a system that enables environmental conservation or simplification of image formation includes a technique of forming an image by heat development.
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of photomechanical processes from the standpoints of environmental protection and space savings. Techniques relating to photosensitive heat-developable photosensitive materials for use in photomechanical processes are required which enables efficient exposure by a laser scanner or a laser image setter and formation of a clear black image having high resolution and sharpness. Such photosensitive heat-developable materials can provide users with a simple and non-polluting heat development processing system that eliminates the use of solution-type processing chemicals.
Methods for forming an image by heat development are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Morgan and B. Shely, Imaging Processes and Materials, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d A, 8th ed., page 2, compiled by Sturge, V. Walworth and A. Shepp, Neblette (1969). The photosensitive material contains a reducible light-insensitive silver source (e.g., organic silver salt), a photocatalyst (e.g., silver halide) in a catalytically active amount, and a reducing agent for silver, which are usually dispersed in an organic binder matrix. This photosensitive material is stable at an ambient temperature, but when the material is heated at a high temperature (e.g., 8xc2x0 C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image generated upon exposure. The silver produced by the reaction of the reducible silver salt in the exposure region provides a black image and this presents a contrast to the non-exposure region to form an image.
Fog is a serious problem for heat-developable photosensitive materials. Various researches have been made to reduce the fog in silver halide photosensitive materials for thermal photography. As an antifoggant, for example, U.S. Pat. No. 3,589,903 discloses use of mercury salts. Furthermore, there have also been disclosed uses of carboxylic acids such as benzoic acid and phthalic acid (U.S. Pat. No. 4,152,160), benzoylbenzoic acid compounds (U.S. Pat. No. 4,784,939), indane or tetralincarboxylic acids (U.S. Pat. No. 4,569,906), dicarboxylic acids (U.S. Pat. No. 4,820,617), heteroaromatic carboxylic acids (U.S. Pat. No. 4,626,500), halogenated compounds (U.S. Pat. Nos. 4,546,075, 4,756,999, 4,452,885, 3,874,946 and 3,955,982), halogen molecules or halogen atoms bonded to heterocycles (U.S. Pat. No. 5,028,523), palladium compounds (U.S. Pat. No. 4,103,312 and British Patent No. 1,502,670), iron family compounds (U.S. Pat. No. 4,128,428), substituted triazoles (U.S. Pat. Nos. 4,123,374, 4,129,557 and 4,125,430), sulfur compounds (U.S. Pat. Nos. 4,213,784, 4,245,033, and JP-A-51-26019 [the abbreviation xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d]), thiouracils (U.S. Pat. No. 4,002,479), sulfinic acid (JP-A-50-123331), metal salts of thiosulfonic acid (U.S. Pat. Nos. 4,125,403, 4,152,160 and 4,307,187), and combinations of metal salts of thiosulfonic acid and sulfinic acid (JP-A-53-20923 and JP-A-53-19825), thiosulfonic acid esters (JP-B-62-50810 [the abbreviation xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d], JP-A-7-209797 and JP-A-9-43760). There has also been disclosed use of disulphide compounds (JP-A-51-42529 and JP-B-63-37368).
However, those compounds have drawbacks, for example, insufficient anti-fog effect, decrease of Dmax and degraded image storage stability after development at a larger addition amount and so forth. Therefore, novel antifoggants have been desired.
In view of those drawbacks of the conventional materials and the existing need, an object of the present invention is to provide a heat-developable photosensitive material which causes extremely low fog (Dmin), in particular, an ultrahigh contrast heat-developable photosensitive material which exhibits low Dmin and is suitable for photomechanical reproduction.
The aforementioned object was achieved by the present invention. The present invention thus provides a heat-developable photosensitive material which comprises, on the same side of a support, at least (a) a photosensitive silver halide, (b) a reducible silver salt, (c) a phenol compound represented by the following general formula (1), (d) a binder, and (e) a coupler compound. 
In the general formula (1) , V1 to V8 each independently represent hydrogen atom or a functional group. L represents a bridging group consisting of xe2x80x94CH(V9)xe2x80x94 or xe2x80x94Sxe2x80x94. V9 represents a hydrogen atom or a functional group.
The coupler compound used for the heat-developable photosensitive material of the present invention preferably consists of one or more of compounds represented by the following general formulae (2) to (14). 
In the general formulae (2) to (14), X1 to X15 each independently represent a hydrogen atom or a functional group. In the general formula (2), R1 and R2 each independently represent an electron withdrawing group. In the general formulae (3) to (14), R3 to R28 each independently represent a hydrogen atom or a functional group. q represents an integer of 0-4.
The heat-developable photosensitive material of the present invention preferably further comprises an ultrahigh contrast agent.
According to the present invention, there can be provided a heat-developable photosensitive material causing almost no fog (Dmin) without degrading maximum density (Dmax) and sensitivity.
The symbol xe2x80x9c-xe2x80x9d used in the present specification indicates a range that includes the numerical values mentioned before and after the symbol.